Hi,
In addition to Sharan's note, if this is something that was working previously , did anything change on your end ?
If this is something that was working previously and other partnerships are working (with Signature), most likely this should not be caused by a JCE patch missing.
What you need to do is to get the SPID sent within the SAMLRequest and validate it to be the same as what is configured in your Partnership.
It is case sensitive so you need to ensure it is configured on your end the same way they are passing it in the SAMLRequest
Regards
Joe